Coronary vessels, partially occluded by plaque, may become totally occluded by thrombus or blood clot causing myocardial infarction, angina, and other conditions. Carotid, renal, peripheral, and other blood vessels can also be restrictive to blood flow and require treatment. A number of medical procedures have been developed to allow for the removal or displacement (dilation) of plaque or thrombus from vessel walls to open a channel to restore blood flow and minimize the risk of myocardial infarction. For example, atherectomy or thrombectomy devices can be used to remove atheroma or thrombus. In cases where infusion of drugs or aspiration of thrombus may be desired, infusion or aspiration catheters can be placed near the treatment site to infuse or aspirate. In cases where the treatment device can be reasonably expected to shed emboli, embolic protection devices can be placed near the treatment site to capture and remove emboli. In other cases, a stent is placed at the treatment site. Both embolic protection devices and stents can be placed in or near the treatment site using delivery catheters.
In percutaneous transluminal coronary angioplasty (PTCA), a guide wire and guide catheter are inserted into the femoral artery of a patient near the groin, advanced through the artery, over the aortic arch, and into a coronary artery. An inflatable balloon is then advanced into the coronary artery, across a stenosis or blockage, and the balloon inflated to dilate the blockage and open a flow channel through the partially blocked vessel region. One or more stents may also be placed across the dilated region or regions to structurally maintain the open vessel. Balloon expandable stents are crimped onto a balloon in the deflated state and delivered to the lesion site. Balloon expansion expands the stent against the lesion and arterial wall. Alternatively, self expanding stents can be restrained in a sheath, delivered to the treatment site, and the sheath removed to allow expansion of the stent.
Embolic protection devices have been developed to prevent the downstream travel of materials such as thrombi, grumous, emboli, and plaque fragments. Devices include occlusive devices and filters. Occlusive devices, for example distal inflatable balloon devices, can totally block fluid flow through the vessel. The material trapped by the inflatable devices can remain in place until removal using a method such as aspiration. However, aspiration cannot remove large particles because they will not fit through the aspiration lumen. Also, aspiration is a weak acting force and will not remove a particle unless the tip of the aspirating catheter is very close to the particle to be removed. During the occlusion, the lack of fluid flow can be deleterious. In coronary applications, the lack of perfusing blood flow can cause angina. In carotids, seizure can result from transient blockage of blood flow. In both coronaries and carotids, it is not possible to predict who will suffer from angina or seizure due to vessel occlusion. If a procedure starts with an occlusive device, it may be necessary to remove it and start over with a filter device.
Occlusive embolic protection devices can also be placed proximal to the treatment site. Debris generated at or near the treatment site will not be transported from the treatment site if a proximal occlusive device substantially stops blood flow through the vessel. The material generated during treatment can remain in place until removal using a method such as aspiration. Generally, proximal occlusive embolic protection devices suffer from many of the same limitations as distal occlusive embolic protection devices.
Other embolic protection devices are filters. Filters can allow perfusing blood flow during the emboli capture process. The filters can advance downstream of a site to be treated and expand to increase the filter area. The filter can capture emboli, such as grumous or atheroma fragments, until the procedure is complete or the filter is occluded. When the filter reaches its capacity, the filter may then be retracted and replaced.
Embolic protection devices can be delivered over wires and within guide catheters. The embolic protection methods are normally practiced ancillary to another medical procedure, for example PTCA with stenting or atherectomy. The embolic protection procedure typically protects downstream regions from emboli resulting from practicing the therapeutic interventional procedure. In the example of PTCA, the treating physician must advance a guide wire through the aorta, over the aortic arch, and into a coronary ostium. Advancing the guide wire through tortuous vessels from a femoral artery approach can be difficult and vary with both the patient and the vessel site to be treated. Guide wires are typically selected by the treating physician, based on facts specific to the patient and therapeutic situation, and also on the training, experiences, and preferences of the physician. In particular, a physician may have become very efficient in using a specific guide wire to identify the left coronary ostium and then advance a balloon catheter over the positioned guide wire. The efficacy of the procedure may depend on the physician being able to use a favored guide wire.
In the example PTCA procedure, a guide catheter extends proximally from the patient's groin area, and may be about 100 centimeters long. A 320 cm guidewire is placed into the guide catheter and extended distal of the guide into a coronary vessel, leaving about a 200 cm long guide wire proximal region extending from the guide catheter. The embolic protection device delivery catheter, nominally about 130 cm in length, can advance over the guide wire and within the guide catheter, until a length of guide wire extends from both the guide catheter and delivery catheter. The guide wire can then be retracted and removed from the patient. In some methods, the embolic protection device then advances through and out of the positioned delivery catheter, to the target site to be protected or filtered. In other methods, delivery is accomplished by disposing the embolic protection filter device within the delivery catheter distal region, and advancing the delivery catheter and embolic protection device together within the guide catheter, optionally over the guide wire, and deploying the filter by retracting the delivery catheter while maintaining the position of the filter, thus forcing the filter distally out of the delivery catheter.
Advancement of the delivery catheter over a single length, nominally 170 cm long guide wire presents a problem. The treating physician can only advance the filter delivery catheter about 40 cm over the guide wire until the delivery catheter advances into the patient and the guide wire is inaccessible within the delivery catheter. The guide wire position should be controlled at all times so as to not be dislodged by the advancing delivery catheter from the hard acquired guide wire position within the patient.
One solution to this problem is to use a guide wire at least double the length of the delivery catheter as described above. A 320 cm long guide wire can extend at least about 150 cm from the patient's groin, having an accessible region exposed at all phases of delivery catheter placement. However, the length of the 320 cm guidewire makes manipulating and rotating the guide wire very difficult for the treating physician. Additional personnel can hold the extra length of the guide wire to prevent the added wire length from falling to the floor, where it would become contaminated. However, not all cardiac catheter laboratories have personnel available to maintain control of the long guide wire. In many labs, the physician is working alone in the sterile field. Advancing a device delivery catheter over a positioned, favored, and short (175 cm) guide wire would be inherently more efficacious than requiring use of an unfamiliar, disfavored, or double length guide wire to position the delivery catheter.
Another alternative catheter design is the monorail or rapid exchange type such as that disclosed in U.S. Pat. No. 4,762,129, issued Aug. 9, 1988, to Bonzel. This catheter design utilizes a conventional inflation lumen plus a relatively short parallel guiding or through lumen located at its distal end and passing through the dilatation balloon. Guide wires used with PTCA balloon catheters are typically 175 cm in length and are much easier to keep within the sterile operating field than 300 to 340 cm guide wires. This design enables the short externally accessible rapid exchange guide wire lumen to be threaded over the proximal end of a pre-positioned guide wire without the need for long guide wires.
Still needed in the art are improved designs for rapid exchange delivery catheters.